Field of the Disclosure
The present disclosure relates to an apparatus for detecting speed of a motor.
Discussion of the Related Art
In general, as variable speed drives of AC (alternating current) motors by inverters are widely used, speed of the motors are detected by attaching a speed detection sensor to the motor, when accurate speed control of the motors is required.
Incremental encoders are commonly used as such speed detection sensors. The incremental encoders may be widely divided into encoders to output square-wave signals and encoders to output sine-wave signals.
Among them, the encoder outputting a sine-wave signal (hereinafter referred to as ‘sine-wave encoder’) outputs a two-phase sine-wave having a predetermined number of ninety-degree phase differences between each other per rotation of a motor. Thus, the sine-wave encoder detects a speed of a motor, by measuring the sine-wave using a speed detecting device provided in an inverter, at every predetermined interval.
However, when detecting a speed of a motor by using a conventional sine-wave encoder, because a high frequency signal is used, there occurs a problem that accuracy of the detected speeds is declined when the speed of the motor is increased.